Several methods are known for depositing a material on a substrate. For instance, substrates may be coated by evaporating, sputtering and chemical vapor deposition. Typically, the process is performed in a process apparatus or process chamber, where the substrate to be coated is located. A deposition material is provided in the apparatus. A plurality of materials, but also oxides, nitrides or carbides thereof, may be used for deposition on a substrate. Further, other processing steps like etching, structuring, annealing, or the like can be conducted in processing chambers.
Coated materials may be used in several applications and in several technical fields. For instance, an application lies in the field of microelectronics, such as generating semiconductor devices. Also, substrates for displays are often coated by a PVD process. Further applications include coating of flexible substrates.
As an example, sputtering is a vacuum coating process used to deposit thin films of various materials onto the surface of a substrate. For example, sputtering can be used to deposit dielectric insulators such as SiO2. During the sputtering process, the coating material is transported from a target to the substrate to be coated by bombarding the surface of the target with ions of an inert gas, which have been accelerated by a high voltage. When the gas ions hit the outer surface of the target, the momentum of the gas ions is transferred to the atoms of the material so that some of the atoms can gain sufficient energy to overcome the binding energy of the atoms in order to escape from the target surface and to deposit on the substrate. The atoms of the material form a film of the desired material. The thickness of the deposited film is, inter alia, dependent on the duration of the substrate's exposure to the sputtering process.
In reactive sputtering, one or more reactive gases such as oxygen and nitrogen could be provided in addition to the inert gas. These gases react with the coating material to form a reaction product, which is deposited on the substrate. Reactive sputtering is particularly used for forming oxides (e.g., SiO2, Al2O3, ZnO), nitrides (e.g., Si3N4, TiN) and oxynitrids (e.g., SiOxNy). Properties and a quality of the coated layers depend particularly on a flow rate and an amount of the reactive gas supplied to the process chamber. Thus, it is important to precisely control the flow rate and amount of the reactive gas into the process chamber.
However, sensors provided within the process chamber for measuring gas parameters (e.g. a partial pressure of the reactive gas) and used for controlling the flow rate can be subject to contamination and drift. Thus, particularly over time, an accuracy of the sensor readings becomes deteriorated. As a consequence, a precise control of the gas flow is not possible anymore. In such a case, the sensors need to be cleaned or even be replaced.
In view of the above, it is an object to provide a method for controlling a gas supply, particularly a method for controlling a gas supply to a process chamber during vacuum layer deposition, which overcomes at least some of the problems in the art.